[jeffbradberry]

There's a great little story by L. Sprague de Camp called "Lest Darkness Fall" that is almost exactly this. An archaeologist from the 1930s gets stuck back in the 6th century A.D., and "invents" the printing press (among other things).

[inklesspen]

Yeah, I've read that. Also "The Man who Came Early" by Poul Anderson and a lot of similar stories.